Can Platys Tolerate Brackish Water?

[Doomchibi]

I had gone to buy a few mollies for my brackish tank and my mother talked me into a little platy as well. Currently they are all in a freshwater tank so they can have a few days rest after being moved, and the platy is welcome to stay in it if it would be happier. I would like to be able to move it simply because otherwise it would be the only fish in the freshwater tank and I figure it would be happier with a larger tank and other fish to live with.  I have been trying to find information about platys and brackish water but am only getting conflicting opinions. 
 
More specifically for a question, Would a platy be able to safely live in a tank at about 1.005 sg, going up to 1.010 sg? I am going to be raising the salinity in that tank while other fish in it grow until they are moved out, after which the salinity is going to be lowered back down to about 1.006 sg, or 1.008 at the highest. 
 
 
Also, off topic question in case anyone happens to know- I have heard of some types of mollies growing to about 4-5", are those sailfin mollies only? The type I have, have shorter fins and are black and white marbled, and I am thinking they probably aren't going to get very big. It's not a huge deal at the moment but I would like an idea of what they're going to reach.

 

[RockabillyGuy]

Sphenopses can grow big as sailfins. But with only difference. Practically always are big-ones females.
Different story is with sailfins. Both sexes are growing, males even more.
 
Platys dont like salt in water. They can tolerate it (NaCl) but if You add seasalt theyr frys stops to grow(or will grow very slowly).

 

[Doomchibi]

Alright, i'll keep the platy in freshwater then. It's also nice to know the mollies are going to get to a decent size, it will help keep the other fish from trying to eat them. I am hoping the platy would be happy enough living by itself for a while though, at least until I found something else to keep it with, but will it eventually become depressed or inactive being alone? I am not sure how social they generally are but I want it to be as comfortable as possible. 

 

[RockabillyGuy]

You have only one platy? Loneliness is not good.

 

[Doomchibi]

Yes, at the moment it is only one. It was the only one at the store in the middle of about 30 rainbow sharks, looked terrified and I thought it was very pretty which is why I was convinced to buy it. I am planning on getting some more community fish to keep with it soon. I have it in my semi aggressive tank right now but all of the fish in it are still very young and small and so it is being left alone currently. It should be out of there within the next week, but for now it is hanging around with my two angelfish. The mollies are in my brackish tank now and have gotten much more active and are eating more, so far so good.